γ-Secretase: Successive Tripeptide and Tetrapeptide Release from the Transmembrane Domain of β-Carboxyl Terminal Fragment

Journal of Neuroscience - Tập 29 Số 41 - Trang 13042-13052 - 2009
Mako Takami1, Yu Nagashima2, Y Sano3, Seiko Ishihara1, Maho Morishima‐Kawashima4, Satoru Funamoto1, Yasuo Ihara1
1Department of Neuropathology, Faculty of Life and Medical Sciences, Doshisha University, Kizugawa 619-0225, Japan
2Department of Neurology, Faculty of Medicine, University of Tokyo, Tokyo 113-0033, Japan,
3Drug Metabolism and Pharmacokinetics Research Section, Eisai Company Ltd., Tsukuba 300-2635, Japan, and
4Department of Molecular Neuropathology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan

Tóm tắt

Amyloid β protein (Aβ), a pathogenic molecule associated with Alzheimer's disease, is produced by γ-secretase, which cleaves the β-carboxyl terminal fragment (βCTF) of β-amyloid precursor protein in the middle of its transmembrane domain. How the cleavage proceeds within the membrane has long been enigmatic. We hypothesized previously that βCTF is cleaved first at the membrane–cytoplasm boundary, producing two long Aβs, Aβ48and Aβ49, which are processed further by releasing three residues at each step to produce Aβ42and Aβ40, respectively. To test this hypothesis, we used liquid chromatography tandem mass spectrometry (LC-MS/MS) to quantify the specific tripeptides that are postulated to be released. Using CHAPSO (3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxyl-1-propanesulfonate)-reconstituted γ-secretase system, we confirmed that Aβ49is converted to Aβ43/40by successively releasing two or three tripeptides and that Aβ48is converted to Aβ42/38by successively releasing two tripeptides or these plus an additional tetrapeptide. Most unexpectedly, LC-MS/MS quantification revealed an induction period, 3–4 min, in the generation of peptides. When extrapolated, each time line for each tripeptide appears to intercept the same point on thex-axis. According to numerical simulation based on the successive reaction kinetics, the induction period exists. These results strongly suggest that Aβ is generated through the stepwise processing of βCTF by γ-secretase.

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Tài liệu tham khảo

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Thông tin xuất bản

Journal of Neuroscience

Tập 29 Số 41

13042-13052

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